Drive circuit for liquid ejecting device and liquid ejecting device

ABSTRACT

A drive circuit of a liquid ejecting device includes a first switch, a second switch, and a signal processing circuit. The first switch is connected between a first potential and an output terminal through which a drive signal is transmitted to an actuator of a liquid ejecting device. The second switch is connected between the output terminal and a second potential lower than the first potential. The signal processing circuit is configured to detect a difference between a waveform of a target drive signal and the drive signal waveform output at the output terminal, and to cause the first switch and the second switch to be off when an absolute value of the difference is less than a threshold value.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2019-037558, filed on Mar. 1, 2019, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a drive circuit for aliquid ejecting device and a liquid ejecting device.

BACKGROUND

A liquid ejecting device that supplies a predetermined amount of liquidto a predetermined position is known. The liquid ejecting device ismounted on, for example, an ink jet printer, a 3D printer, or a liquiddispensing device. An ink jet printer ejects ink droplets from an inkjet head to print an image or the like on a surface of a recordingmedium, such as a sheet of paper. A 3D printer ejects droplets of apattern forming material from a material ejection head and the ejecteddroplets are then cured to form a three-dimensional object. A liquiddispensing device supplies a predetermined amount of a sample materialto each of a plurality of containers or the like.

An ink jet printer of one type includes an on-demand ink jet head thatejects ink from a nozzle. The ink is ejected from the nozzle by applyinga drive signal of a common drive waveform (generated by pulse widthmodulation (PWM) driving) to a piezoelectric actuator that is selectedfrom a plurality of piezoelectric actuators according to print data(e.g., image or pattern data). In PWM driving, a transistor of an outputswitch is switched by a triangular wave even when the common drivewaveform is sufficiently close to a target drive waveform, and thusunnecessary power is consumed. In order to improve ink ejectioncharacteristics or to increase the gradation of dots, the common drivewaveform can be set to be a waveform in which flat portions and slopesare combined in various ways. Therefore, it is difficult to suppressunnecessary switching of a waveform including a slope where a voltage isincreased or decreased.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an overall configuration of an ink jetprinter according to a first embodiment.

FIG. 2 illustrates a perspective view of an ink jet head of the ink jetprinter.

FIG. 3 illustrates a plan view of a nozzle plate of the ink jet head.

FIG. 4 illustrates a longitudinal cross-sectional view of the ink jethead.

FIG. 5 illustrates a longitudinal cross-sectional view of the nozzleplate of the ink jet head.

FIG. 6 is a block diagram illustrating a configuration of a controlsystem of the ink jet printer.

FIG. 7 is a diagram illustrating a drive signal that is applied to anactuator of the ink jet head.

FIGS. 8A to 8E are diagrams illustrating operations of the actuator towhich the drive signal is applied.

FIG. 9 is a circuit diagram illustrating an ink jet head drive circuitaccording to the first embodiment.

FIG. 10 is a diagram illustrating a maximum amplitude of a drivewaveform.

FIG. 11 is a circuit diagram illustrating a load counting circuit of theink jet head drive circuit.

FIG. 12 is a diagram illustrating waveform elements for which the loadcounting circuit of the ink jet head drive circuit counts the number ofloads.

FIG. 13 is a diagram illustrating waveform elements for which the loadcounting circuit of the ink jet head drive circuit counts the number ofloads.

FIG. 14 is diagram illustrating switching of an output switch when thesensitivity of pulse width modulation changes depending on the size of aload.

FIG. 15 is diagram illustrating the switching of an output switch whenthe sensitivity of pulse width modulation changes depending on size of aload.

FIGS. 16A to 16C are graphs illustrating a simulation result of PWM whena dead band is provided.

FIGS. 17A and 17B are graphs illustrating a simulation result of PWMwhen a dead band is not provided.

FIG. 18 is a circuit diagram illustrating an ink jet head drive circuitaccording to a second embodiment.

FIG. 19 is a circuit diagram illustrating an ink jet head drive circuitaccording to a third embodiment.

FIG. 20 is a circuit diagram illustrating an ink jet head drive circuitaccording to a fourth embodiment.

FIG. 21 illustrates a longitudinal cross-sectional view of an ink jethead according to a modification example.

DETAILED DESCRIPTION

In general, according to an embodiment, a drive circuit for a liquidejecting device includes a first switch, a second switch, and a signalprocessing circuit. The first switch is connected between a firstpotential and an output terminal at which a drive signal waveform istransmitted to an actuator of a liquid ejecting device. The secondswitch is connected between the output terminal and a second potentiallower than the first potential. The signal processing circuit cause thefirst switch and the second switch to stay be off when an absolute valueof a difference between a target drive signal waveform and the drivesignal waveform at the output terminal is less than a threshold value.

Hereinafter, a drive circuit for a liquid ejecting device and an imageforming apparatus according to certain example embodiments will bedescribed with reference to the accompanying drawings. In the respectivedrawings, the same components/aspects will be represented by the samereference numerals.

First Embodiment

An ink jet printer 10 that prints an image on a recording medium will bedescribed as an example of an image forming apparatus on which a liquidejecting device 1 according to a first embodiment can be mounted. FIG. 1illustrates a schematic configuration of the ink jet printer 10. The inkjet printer 10 includes, for example, a box-shaped housing 11 that isalso referred to as an external body. In housing 11, a cassette 12 thataccommodates a sheet S, which is an example of a recording medium, anupstream conveyance path 13 of the sheet S, a conveyance belt 14 thatconveys the sheet S picked up from the cassette 12, ink jet heads 1A to1D that eject ink droplets to the sheet S on the conveyance belt 14, adownstream conveyance path 15 of the sheet S, a discharge tray 16, and acontrol substrate 17 are arranged. An operation unit 18 that is a userinterface is arranged in an upper portion of the housing 11.

Image data to be printed on the sheet S is generated by, for example, acomputer 2 that is an external apparatus. The image data generated bythe computer 2 is transmitted to the control substrate 17 of the ink jetprinter 10 through a cable 21 and connectors 22B and 22A.

A pickup roller 23 supplies the sheets S from the cassette 12 to theupstream conveyance path 13 one by one. Along the upstream conveyancepath 13, feed roller pairs 13 a and 13 b and sheet guide plates 13 c and13 d are provided. The sheet S is conveyed to an upper surface of theconveyance belt 14 through the upstream conveyance path 13. In thedrawing, arrow A1 indicates a conveyance path of the sheet S from thecassette 12 to the conveyance belt 14.

The conveyance belt 14 is an endless belt comprising a mesh materialhaving a plurality of through holes on a surface. Three rollersincluding a driving roller 14 a and driven rollers 14 b and 14 c supportthe conveyance belt 14 such that the conveyance belt 14 is rotatable. Amotor 24 rotates the driving roller 14 a to rotate the conveyance belt14. The motor 24 is an example of a driving device. In the drawing, A2indicates a rotation direction of the conveyance belt 14. On a backsurface of the conveyance belt 14, a negative pressure container 25 isarranged. The negative pressure container 25 is connected to a fan 26for depressurization and adjusts the inside of the container to be in anegative pressure using air flow formed by the fan 26. Since the insideof the negative pressure container 25 is adjusted to be in a negativepressure container, the sheet S is adsorbed and held on the uppersurface of the conveyance belt 14. In the drawing, A3 indicates the flowof air flow.

The ink jet heads 1A, 1B, 1C, and 1D are arranged to face the sheet S onthe conveyance belt 14 across a small gap of, for example, 1 mm. The inkjet heads 1A to 1D each eject ink droplets on to the sheet S. When thesheet S passes below the ink jet heads 1A to 1D, an image is printed onthe sheet S. The ink jet heads 1A to 1D have the same structure exceptthat the colors of inks to be ejected are different from each other. Thecolors of the inks are, for example, cyan, magenta, yellow, and black.

The ink jet heads 1A, 1B, 1C, and 1D are connected to corresponding inktanks 3A, 3B, 3C, and 3D and ink supply pressure adjusting devices 32A,32B, 32C, and 32D through ink flow paths 31A, 31B, 31C, and 31D,respectively. The ink flow paths 31A to 31D are, for example, tubesformed of a resin. The ink tanks 3A to 3D are containers where the inksare stored. The ink tanks 3A to 3D are arranged above the ink jet heads1A to 1D, respectively. In a sleep mode, the ink supply pressureadjusting devices 32A to 32D adjust the ink jet heads 1A to 1D to have anegative pressure internally of, for example, −1 kPa with respect to theatmospheric pressure, such that leakage of inks from nozzles (refer toFIG. 2) of the ink jet heads 1A to 1D is prevented. During imageformation, the inks of the ink tanks 3A to 3D are supplied to the inkjet heads 1A to 1D by the ink supply pressure adjusting devices 32A to32D, respectively.

After image formation, the sheet S is conveyed from the conveyance belt14 to the downstream conveyance path 15. Along the downstream conveyancepath 15, feed roller pairs 15 a, 15 b, 15 c, and 15 d, and sheet guideplates 15 e and 15 f that regulate the conveyance path of the sheet Sare provided. The sheet S is conveyed from a discharge port 27 to adischarge tray 16 through the downstream conveyance path 15. In FIG. 1,arrow A4 indicates the conveyance path of the sheet S.

Next, a configuration of the ink jet head 1A will be described withreference to FIGS. 2 to 6. Since the ink jet heads 1B to 1D have thesame structure as that of the ink jet head 1A, the detailed descriptionthereof will not be repeated.

FIG. 2 illustrates a perspective view of the ink jet head 1A. The inkjet head 1A includes an ink supply unit 4 as an example of the liquidsupply unit, a nozzle plate 5, a flexible substrate 6, and a head drivecircuit 7. A plurality of nozzles 51 that eject ink are arranged in thenozzle plate 5. The ink that is ejected from the respective nozzles 51is supplied from the ink supply unit 4 communicating with the nozzles51. The ink flow path 31A from the ink supply pressure adjusting device32A is connected to an upper side of the ink supply unit 4. Arrow A2indicates a rotation direction of the above-described conveyance belt 14(refer to FIG. 1).

FIG. 3 illustrates a partially enlarged plan view of the nozzle plate 5.The nozzles 51 are two-dimensionally arranged in a column direction (Xdirection) and a row direction (Y direction). In this case, the nozzles51 arranged in the row direction (Y direction) are obliquely arrangedsuch that the nozzles 51 do not overlap each other on an axis line ofthe Y-axis. The nozzles 51 are arranged at an interval of a distance X1in the X-axis direction and at an interval of a distance Y1 in theY-axis direction. For example, the distance X1 is about 42.25 μm, andthe distance Y1 is about 253.5 μm. That is, the distance X1 isdetermined such that the recording density in the X-axis direction is600 DPI. Further, the distance Y1 is also determined such that printingis performed at 600 DPI in the Y-axis direction. Eight nozzles 51arranged in the Y direction are set as one set, and plural sets ofnozzles 51 are arranged in the X direction. Although not specificallydepicted in the drawing, for example, 150 sets of nozzles 51 arearranged in the X direction, and 1200 nozzles 51 in total are arranged.

A piezoelectric actuator 8 (hereinafter, simply referred to as “actuator8”) as an example of a capacitive actuator that is a drive source in anoperation of ejecting ink. In this example, an actuator 8 is providedfor each of the nozzles 51. These actuators 8 are formed in an annularshape and are arranged such that the nozzles 51 are positioned at thecenters thereof. One set of nozzles 51 and the actuators 8 form onechannel. Regarding the size of the actuator 8, for example, the innerdiameter is 30 μm, and the outer diameter is 140 μm. The actuators 8 areelectrically connected to individual electrodes 81, respectively.Further, eight actuators 8 arranged in the Y direction are electricallyconnected to each other through a common electrode 82. The individualelectrodes 81 and the common electrode 82 are further electricallyconnected to mounting pads 9, respectively. The mounting pad 9 functionsas an input port that applies a drive signal (electrical signal) of adrive waveform to the actuator 8. The individual electrodes 81 applydrive waveforms to the actuators 8, respectively, and each of theactuators 8 is driven according to the applied drive waveform. Forconvenience of description, the actuators 8, the individual electrodes81, the common electrodes 82, and the mounting pads 9 are indicated bysolid lines in FIG. 3, but are arranged in the nozzle plate 5 (refer toa longitudinal cross-sectional view of FIG. 4). Of course, the positionof the actuator 8 is not limited to the inside of the nozzle plate 5.

The mounting pad 9 is electrically connected to a wiring pattern formedon the flexible substrate 6 through, for example, an anisotropic contactfilm (ACF). Further, the wiring pattern of the flexible substrate 6 iselectrically connected to the head drive circuit 7. The head drivecircuit 7 is, for example, an integrated circuit (IC). The head drivecircuit 7 applies the drive waveform to the actuator 8 selectedaccording to print data.

FIG. 4 illustrates a longitudinal cross-sectional view of the ink jethead 1A. As illustrated in FIG. 4, the nozzle 51 penetrates into thenozzle plate 5 in a Z-axis direction. Regarding the size of the nozzle51, for example, the diameter is 20 μm, and the length is 8 μm. In theink supply unit 4, a plurality of pressure chambers (individual pressurechambers) 41 that communicate with the nozzles 51, respectively, areprovided. The pressure chamber 41 is, for example, a cylindrical spacehaving an open upper portion. The upper portion of each of the pressurechambers 41 is open and communicates with a common ink chamber 42. Theink flow path 31A communicates with the common ink chamber 42 through anink supply port 43. The respective pressure chambers 41 and the commonink chamber 42 are filled with ink. The common ink chamber 42 may beformed, for example, in the shape of a flow path through which ink iscirculated. The pressure chamber 41 has a configuration in which, forexample, a cylindrical hole having a diameter of 200 μm is formed in,for example, a single-crystal silicon wafer having a thickness of 500μm. The ink supply unit 4 has a configuration in which a spacecorresponding to the common ink chamber 42 is formed in, for example,alumina (Al₂O₃).

FIG. 5 illustrates a partially enlarged view of the nozzle plate 5. Thenozzle plate 5 has a structure in which a protective layer 52, theactuator 8, and a diaphragm 53 are laminated in this order from thebottom surface. The actuator 8 has a structure in which a lowerelectrode 84, a thin plate-shaped piezoelectric body 85 that is anexample of a piezoelectric element, and an upper electrode 86 arelaminated. The upper electrode 86 is electrically connected to theindividual electrode 81, and the lower electrode 84 is electricallyconnected to the common electrode 82. At a boundary between theprotective layer 52 and the diaphragm 53, an insulating layer 54 thatprevents short-circuiting between the individual electrode 81 and thecommon electrode 82 is interposed. The insulating layer 54 is formed of,for example, a silicon dioxide film (SiO₂) having a thickness of 0.5 μm.The lower electrode 84 and the common electrode are electricallyconnected to each other through a contact hole 55 formed in theinsulating layer 54. The piezoelectric body 85 is formed of, forexample, lead zirconate titanate (PZT) having a thickness of 5 μm orless in consideration of piezoelectric characteristics and dielectricbreakdown voltage. The upper electrode 86 and the lower electrode 84 areformed of, for example, platinum having a thickness of 0.15 μm. Theindividual electrode 81 and the common electrode 82 are formed of, forexample, gold (Au) having a thickness of 0.3 μm.

The diaphragm 53 is formed of an insulating inorganic material. Theinsulating inorganic material is, for example, silicon dioxide (SiO₂).The thickness of the diaphragm 53 is, for example, 2 μm to 10 μm andpreferably 4 μm to 6 μm. The diaphragm 53 and the protective layer 52are curved inward by d31 mode deformation of the piezoelectric body 85when a voltage is applied to the piezoelectric body 85. When theapplication of a voltage to the piezoelectric body 85 is stopped, thediaphragm 53 and the protective layer 52 return to the original states.Due to this reversible deformation, the volume of a pressure chamber) 41expands and contracts. When the volume of the pressure chamber 41changes, the ink pressure in the pressure chamber 41 changes.

The protective layer 52 is formed of, for example, polyimide having athickness of 4 μm. The protective layer 52 covers one surface of thebottom surface side of the nozzle plate 5 and further covers an innercircumferential surface of a hole of the nozzle 51.

FIG. 6 is a block diagram illustrating a configuration of a controlsystem of the ink jet printer 10. On the control substrate 17 as thecontrol unit of the printer, a CPU 90, a ROM 91, a RAM 92, an I/O port93 as an input/output port, and an image memory 94 are mounted. The CPU90 controls the drive motor 24, the ink supply pressure adjustingdevices 32A to 32D, the operation unit 18, and various sensors throughthe I/O port 93. The image data from the computer 2 as the externalconnection apparatus is transmitted to the control substrate 17 throughthe I/O port 93 and is stored in the image memory 94. The CPU 90 loadsthe image data stored in the image memory 94 to, for example, a dotpattern and transmits the image data to the head drive circuit 7 for ofprinting. The head drive circuit 7 applies a drive waveform to theactuator 8 selected according to the image data.

Next, the drive waveform applied to the actuator 8 and an operation ofthe actuator 8 that ejects ink from the nozzles 51 will be describedwith reference to FIGS. 7 and 8. FIG. 7 illustrates, as an example ofthe drive waveform, a waveform of a single pulse. However, the drivewaveform is not limited to a single pulse. For example, a multi-dropmethod such as a double pulse or a triple pulse by which ink dropletsare dropped multiple times during one drive period may be adopted. Thedrive waveform of FIG. 7 is a so-called pull waveform but in otherexamples may be a push waveform or a pull-push waveform.

The head drive circuit 7 applies a bias voltage V1 to the actuator 8from time t0 to time t1. That is, the voltage V1 is applied between theupper electrode 86 and the lower electrode 84. The voltage to be appliedis decreased to a voltage V0 (e.g., voltage V0=0 V), and the voltage V0is applied from time t2 to time t3. Next, the voltage to be applied isincreased to a voltage V2, and the voltage V2 is applied from time t4 totime t5 so as to eject ink. After the end of ejection, the voltage to beapplied is increased up to the voltage V1 to attenuate residualvibration in the pressure chamber 41. The voltage V2 is lower than thebias voltage V1, and the voltage value of voltage V1 is determined basedon, for example, an attenuation rate of the pressure vibration of theink in the pressure chamber 41. For example, the length of the period oftime from time t1 to time t3 and the length of the period of time fromtime t3 to time t5 are respectively set to a half-period of a naturalvibration period λ, which depends on ink characteristics and the inkjethead internal structure. The half-period of the natural vibration periodλ is also referred to as “acoustic length (AL)”. During the series ofoperations, the voltage of the common electrode 82 is fixed to zero (0)V.

FIGS. 8A to 8E schematically illustrates an operation of driving theactuator 8 using the drive waveform illustrated in FIG. 7 to eject inkfrom a nozzle 51. In a sleep mode, the pressure chamber 41 is filledwith ink. A meniscus position of the ink in the nozzle 51 remains in thevicinity of about 0 (i.e., near the nozzle 51 exit) as illustrated inFIG. 8A. When the bias voltage V1 is applied as a contraction pulseduring the period from time t0 to time t1, an electric field isgenerated in a thickness direction of the piezoelectric body 85, and d31mode deformation occurs in the piezoelectric body 85 as illustrated inFIG. 8B such that the actuator 8 is curved inward (toward pressurechamber 41). That is, the actuator 8 is deformed such that the volume ofthe pressure chamber 41 contracts.

At time t2, when the voltage V0 (voltage V0=0 V) is applied as anexpansion pulse, the actuator 8 returns to a non-deformed state asschematically illustrated in FIG. 8C. At this time, in the pressurechamber 41, the volume returns to the original volume such that the inkpressure in the pressure chamber 41 decreases. When the ink is suppliedfrom the common ink chamber 42, the ink pressure increases. Next, attime t3, the supplying of the ink to the pressure chamber 41 is stoppedsuch that the increase in ink pressure is also stopped. That is, thepulse is in a so-called pull state.

At time t4, when the voltage V2 is applied as a contraction pulse, asschematically illustrated in FIG. 8D, the piezoelectric body 85 of theactuator 8 is again deformed such that the volume of the pressurechamber 41 contracts. As described above, the ink pressure increasesduring the period from time t2 to time t3. Furthermore, by the pressingof the actuator 8 such that the volume of the pressure chamber 41decreases, the ink pressure increases, and the ink is ejected out fromthe nozzle 51. The application of the voltage V2 continues until timet5, and a droplet of the ink is ejected from the nozzle 51 asschematically illustrated in FIG. 8E.

After the ink is ejected, the voltage V1 is applied as a cancel pulse attime t6. The ink pressure in the pressure chamber 41 decreases when adroplet is ejected. However, the vibration associated with ejection ofthe ink remains in the pressure chamber 41. Therefore, by increasing thevoltage from the voltage V2 to the voltage V1, the actuator 8 is drivensuch that the volume of the pressure chamber 41 contracts, the inkpressure in the pressure chamber 41 becomes substantially zero (0), andthe residual vibration of the ink in the pressure chamber 41 is forciblyattenuated.

The drive waveform illustrated in FIG. 7 is merely exemplary. Bychanging an inclination (dV/dt) of the slope when the voltage isincreased or decreased, the pulse height, or the like in various ways,the size of printed dots can be changed. Furthermore, the drive waveformillustrated in FIG. 7 is a single drive waveform. By sequentiallyarranging a plurality of similar drive waveforms or waveform elementshaving the same waveform or other waveforms to generate a common drivewaveform (refer to FIGS. 12 and 13 described below), then selectivelyapplying these drive waveforms or waveform elements from the commondrive waveform to an actuator 8, dots having various sizes can beformed.

FIG. 9 is a diagram illustrating an overall configuration of an ink jethead drive circuit 100 that generates a drive waveform COM as a commondrive waveform and then applies this generated drive waveform COM to theactuators 8 selectively according to the image data (or other intendedoutput data). The ink jet head drive circuit 100 is an example of adrive circuit for a liquid ejecting device 1. The ink jet head drivecircuit 100 includes: the head drive circuit 7; a switching type commondrive waveform generation circuit 101 that generates the drive waveformCOM by PWM driving; and a load counting circuit 102. The common drivewaveform generation circuit 101 and the load counting circuit 102 can bedisposed on the control substrate 17, for example, as a control unit ofa printer.

The head drive circuit 7 includes a shift register 71, a latch circuit72, a level shifter 73, and a select switch 74. The select switch 74comprises, for example, a transistor that is provided for each of theactuators 8. The control unit of the printer on the control substrate 17loads the image data in the image memory 94 as a dot pattern andtransmits, for example, image data corresponding to the number ofnozzles 51 in FIG. 3 to the shift register 71 in synchronization with aclock signal (SCK). Signals corresponding to the image data that areapplied to the shift register 71 may include a control signal (SI & SPsignal) indicating which actuator 8 is to be supplied with the drivewaveform COM at which time. Further, for example, a gradation of dotscan be designated, for example, using a bit signal such as 2 bits (1,0).Printing at the designated gradation can be implemented by changing thesize of ink droplets or the number of droplets, for example, using amethod including: sequentially arranging a plurality of drive waveformsor waveform elements having the same waveform or different waveforms togenerate a drive waveform COM (refer to FIGS. 12 and 13); andselectively applying one or more drive waveforms or waveform elementsfrom the drive waveform COM to particular actuators 8 according to theimage data or the like.

In addition, the control unit of the printer on the control substrate 17supplies signal LATCH (including a latch signal and a channel signal) tothe latch circuit 72. The latch circuit 72 latches a signal stored inthe shift register 71 at a timing of the latch signal. The level shifter73 converts the signal latched by the latch circuit 72 into a voltagesignal at a level at which the select switch 74 can be turned on andoff. As a result, a select switch 74 that is connected to the actuator 8of the nozzle 51 ejecting the ink is turned on, and the drive waveformCOM generated by the common drive waveform generation circuit 101 isthereby applied to the actuator 8. In the drawing, HGND represents aground terminal of the actuators 8.

The switching type common drive waveform generation circuit 101 isdriven by PWM such that the drive waveform COM applied to the actuator 8is a waveform corresponding to a target drive waveform WCOM. That is, afeedback control is performed such that, when the target drive waveformWCOM is an analog signal, the drive waveform COM and the target drivewaveform WCOM are the same and, when the target drive waveform WCOM is adigital signal, the drive waveform COM and the target drive waveformWCOM are similar to each other. The common drive waveform generationcircuit 101 includes: a switching circuit 107 as an output switch; aninductor L; a feedback line 113 and a filter 108 as an example of thevoltage waveform detection unit that detects the voltage waveform COM tobe applied to the actuator 8; and a digital signal processing unit 120.That is, the voltage waveform detection unit detects a voltage waveformgenerated from a capacitive actuator. The filter 108 filters thedetected voltage waveform. A capacitor Cc is a stabilizing capacitor forstabilizing the feedback control. The digital signal processing unit 120further includes a waveform memory 103 as a storage unit of the targetdrive waveform WCOM, a subtraction/comparison unit 104 as an arithmeticcircuit, a comparator 105, a triangular wave generation circuit 106, andan A/D (analog-digital) converter 109. The comparator 105 functions as apulse width modulation circuit. The switching circuit 107 furtherincludes a gate driver circuit 110, a high side switch SW1 connected toa power supply Vdd, and a low side switch SW2 connected to the ground.

The waveform memory 103 stores information of the target drive waveformWCOM in, for example, as digital data. The waveform memory 103 appliesthe target drive waveform WCOM to an input terminal (A) of thesubtraction/comparison unit 104. The filter 108 smooths the drivewaveform COM fed back from a common line, and the A/D converter 109converts the drive waveform COM smoothed by the filter 108 into adigital signal to generate a comparative drive waveform dCOM. Thecomparative drive waveform dCOM is applied to an input terminal (B) ofthe subtraction/comparison unit 104.

The subtraction/comparison unit 104 performs subtraction comparison(A−B) between the target drive waveform WCOM and the comparative drivewaveform dCOM. When an error is present between the target drivewaveform WCOM and the comparative drive waveform dCOM as a result of thesubtraction comparison, the subtraction/comparison unit 104 applies anerror dWCOM output from an output terminal (A−B) to an input terminal(+) of the comparator 105. When the value of the comparative drivewaveform dCOM is less than the value of the target drive waveform WCOM,the error dWCOM is a positive value, and when the value of thecomparative drive waveform dCOM is more than the value of the targetdrive waveform WCOM, the error dWCOM is a negative value. On the otherhand, when the absolute value of the error dWCOM is in a predeterminedrange as a result of the subtraction comparison (including when no erroris present), the subtraction/comparison unit 104 applies a disablesignal as a stop signal output from an output terminal (A≈B) to the gatedriver circuit 110 of the switching circuit 107. The comparative drivewaveform that is compared to the target drive waveform is notparticularly limited to a filtered digital waveform as long as itrepresents a voltage waveform to be applied to the actuator 8.

While the disable signal is applied, the gate driver circuit 110 turnsoff the high side switch SW1 and the low side switch SW2. That is, theswitching of the output switch is stopped. In addition, the absolutevalue of the error dWCOM being in the predetermined range represents,for example, being within 10% or 5% of the maximum amplitude of thetarget drive waveform WCOM. For example, when the drive waveform of FIG.7 is the target drive waveform WCOM, a pulse height A illustrated inFIG. 10 is the maximum amplitude of the target drive waveform WCOM. Whenthe absolute value of the error dWCOM is within 10% or 5% of the maximumamplitude, the disable signal as the stop signal is applied to the gatedriver circuit 110. This way, by providing a dead band where theswitching of the output switch is stopped, unnecessary switching thatmay be performed when the drive waveform COM is in the vicinity of thetarget drive waveform WCOM can be suppressed, and power consumption canbe reduced. In particular, not only when the voltage of the target drivewaveform WCOM is at a flat portion but also when the voltage of thetarget drive waveform WCOM is at an inclined (dV/dt) slope at which thevoltage is increased or decreased, unnecessary switching can besuppressed.

In the comparator 105, the error dWCOM is input to an input terminal(+), and a triangular wave Tri having a predetermined frequency isapplied to an input terminal (−). The comparator 105 as the pulse widthmodulation circuit compares the error dWCOM to the triangular wave Triand modulates a pulse signal MCOM. The pulse signal MCOM is applied tothe gate driver circuit 110. The gate driver circuit 110 switches on andoff the high side switch SW1 and the low side switch SW2 according tothe applied pulse signal MCOM. The high side switch SW1 and the low sideswitch SW2 are, for example, MOS transistors, and a reflux diode isinserted in parallel with the MOS transistor. The high side switch SW1and the low side switch SW2 are not necessarily connected to the powersupply Vdd and the ground. That is, the high side switch SW1 and the lowside switch SW2 may be a first switch connected to a first potential anda second switch connected to a second potential.

Signal ACOM is output from the switching circuit 107 and is convertedinto the drive waveform COM through the inductor L, and the drivewaveform COM is applied to the select switch 74. As described above, theselect switch 74 that is connected to the actuator 8 selected accordingto the image data is turned on, and the drive waveform COM is appliedthereto. When the drive waveform COM is applied, the operation of theactuator 8 is as describe above.

The load counting circuit 102 counts the number of actuators 8 drivenduring the same period as the number of loads. The load counting circuit102 is an example of the load number detection unit. Being driven duringthe same period represents not only a case where drive timings areexactly the same (simultaneous) but also a case where charge/dischargeperiods of the actuators 8 partially overlap each other even when thedrive timings are different from each other. For example, in the case ofa binary head, the number of loads is the total number of actuators 8driven within the same period. FIG. 11 illustrates an example of acircuit of the load counting circuit 102 including a counter and a latchin the case of a binary head. In the case of binary data, for example,the number of bits 1 input to the shift register 71 is counted while thelatch 72 is latched, and this value can be stored as load numberinformation. On the other hand, for example, in the case of a grayscalehead, one dot is formed when the actuator 8 is charged and dischargedmultiple times in succession. Therefore, as illustrated in examples ofFIGS. 12 and 13, the number of loads for each section of waveformelements constituting a dot instead of for each dot is counted.

In the example of FIG. 12, the target drive waveform WCOM is a referencevoltage waveform including three waveform elements that arechronologically arranged. In this case, the number of loads for eachsection of each waveform element instead of for the entire referencevoltage waveform is counted. In addition, in the example of FIG. 13, inthe target drive waveform WCOM, waveform elements of first to fourthpulses having different waveforms are chronologically arranged. Byselecting one or more pulses from the first to fourth pulses andapplying the selected pulses to the actuator 8, dots having varioussizes are formed. Even in this case, the number of loads for eachsection of each pulse (each waveform element) is counted. Regarding thecounting of the number of loads, for example, the number of loads thatare charged and discharged during the same period is counted from thesignal latched by the latch circuit 72. The load counting circuit 102applies the counted number of loads to an amplitude adjusting input ofthe triangular wave generation circuit 106 as the load numberinformation.

Referring back to FIG. 9, the triangular wave generation circuit 106generates the triangular wave Tri having an amplitude that is adjustedaccording to the number of loads. Specifically, when the number of loadsis large, that is, when the total load is high, the amplitude of thetriangular wave Tri is decreased. When the number of loads is small,that is, when the total load is low, the amplitude of the triangularwave Tri is increased. The size of the amplitude may be determined bythe control unit of the printer as the control substrate 17. Forexample, information (for example, database or a correlation equation)regarding a set value where the number of loads and the amplitude areassociated with each other is generated in advance and is stored in theROM 91 or the like such that the size of the amplitude can be determineddepending on the load number information from the load counting circuit102. It is preferable that the information regarding the set value wherethe number of loads and the amplitude are associated with each other isset to a one-to-one relationship between the number of loads and theamplitude. However, for example, a set value having one amplitude may beassigned to every 100 values of the number of loads in a step-by-stepmanner.

The size of the amplitude of the triangular wave Tri determines thesensitivity to the error dWCOM. Accordingly, when the amplitude of thetriangular wave Tri changes depending on the number of loads, thesensitivity of PWM can be changed depending on the size of the load.Specifically, in a case where the amplitude of the triangular wave Triincreases, when the error dWCOM is changed, a change in pulse width issmall, that is, the sensitivity to the error dWCOM is low. In otherwords, when the amplitude of the triangular wave Tri increases, PWMbecomes shallow. Contrarily, in a case where the amplitude of thetriangular wave Tri decreases, when the error dWCOM is changed, a changein pulse width is large, that is, the sensitivity to the error dWCOM ishigh. In other words, when the amplitude of the triangular wave Tridecreases, PWM becomes deep. This way, when the sensitivity of PWMchanges depending on the size of the load, the operation will bedescribed in detail with reference to FIGS. 14 to 15. FIG. 14illustrates an operation when the load is high and an operation when theload is low in a case where the error dWCOM is a positive value(WCOM>dCOM). FIG. 15 illustrates an operation when the load is high andan operation when the load is low in a case where the error dWCOM is anegative value (WCOM<dCOM). In each of the drawings, a range of A≈Brepresents a range of a dead band when the above-described disablesignal is applied to the gate driver circuit 110 and both the high sideswitch SW1 and the low side switch SW2 are turned off.

While the actuator 8 is charged, for example, as illustrated in FIG. 14,the error dWCOM and the triangular wave Tri are compared to each other,and the high side switch SW1 is turned on during a period where theerror dWCOM is not in the range of dead band and is higher than thetriangular wave Tri. By turning on the high side switch SW1 andconnecting the high side switch SW1 to the power supply Vdd, charge issupplied to the actuator 8 connected to the select switch 74 that isturned on through the inductor L. On the other hand, the high sideswitch SW1 is turned off during a period where the error dWCOM is lowerthan the triangular wave Tri. At this time, the supply of charge to theactuator 8 is continued by reflux through the reflux diode inserted inparallel into the low side switch SW2. This switching is repeated duringthe period of the triangular wave Tri.

When the high side switch SW1 is turned off during a period where theactuator 8 is charged, the output ACOM of the switching circuit 107decreases to be lower than the ground potential by electromotive forcegenerated by the inductor L. Therefore, during this period, there is nointerference with the operation irrespective of whether the low sideswitch SW2 is turned on or off. In this embodiment, in order to simplifythe description, both the high side switch SW1 and the low side switchSW2 are turned off while A≈B. However, in order to reduce the ONresistance during reflux, the gate voltage may be controlled such thatthe low side switch SW2 is turned on during a period where the currentrefluxes through the reflux diode on the low side switch SW2 side.

While the actuator 8 is discharged, for example, as illustrated in FIG.15, the error dWCOM and the triangular wave Tri are compared to eachother, and the low side switch SW2 is turned on during a period wherethe error dWCOM is not in the range of dead band and is lower than thetriangular wave Tri. By turning on the low side switch SW2 andconnecting the low side switch SW2 to the ground, charge flows out fromthe actuator 8 connected to the select switch 74 that is turned onthrough the inductor L. On the other hand, the low side switch SW2 isturned off during a period where the error dWCOM is higher than thetriangular wave Tri. At this time, the outflow of charge from theactuator 8 is continued by reflux through the reflux diode inserted inparallel into the high side switch SW1. This switching is repeatedduring the period of the triangular wave Tri.

When the low side switch SW1 is turned off during a period where theactuator 8 is discharged, the voltage waveform COM increases to behigher than a power supply voltage by electromotive force generated fromthe inductor L. Therefore, during this period, there is no interferencewith the operation irrespective of whether the high side switch SW1 isturned on or off. In this embodiment, in order to simplify thedescription, both the high side switch SW1 and the low side switch SW2are turned off while A≈B. However, in order to reduce the ON resistanceduring reflux, the gate voltage may be controlled such that the highside switch SW1 is turned on during a period where the current refluxesthrough the reflux diode on the high side switch SW1 side.

Here, when the error dWCOM is a positive value (WCOM>dCOM), it isnecessary to increase the output. When the number of actuators 8 drivenduring the same period is large, that is, when the total load is highand the load capacitance is high, a relatively longer time is requiredfor the output to rise. Therefore, a required ON period of the high sideswitch SW1 is longer. In this case, unless the sensitivity of PWM to theerror dWCOM is set to be high, the drive waveform COM cannot follow thetarget drive waveform WCOM. Conversely, when the number of actuators 8driven during the same period is small, that is, when the total load islow and the load capacitance is low, the output rises within a shorterperiod. Therefore, a required ON period of the high side switch SW1 isshorter. In this case, when the sensitivity of PWM to the error dWCOM islow, the actuator 8 is stable.

When the error dWCOM is a negative value (WCOM>dCOM), the same can beapplied. When the load is high and the load capacitance is high, unlessthe sensitivity of PWM to the error dWCOM is set to be high, the drivewaveform COM cannot follow the target drive waveform WCOM. Conversely,in a case where the load is low and the load capacitance is low, whenthe sensitivity of PWM to the error dWCOM is low, the actuator 8 isstable.

This way, the amplitude of the triangular wave Tri changes depending onthe number of loads of the actuators 8 driven during the same period,that is, the sensitivity of PWM changes depending on the number ofloads. As a result, the actuators 8 as capacitive loads can be stablydriven whether the number of actuators 8 driven during the same periodis small or large. Further, when the size of loads that are charged anddischarged during the same period is detected and the sensitivity of PWMis adjusted according to the size of the load, feedback can bestabilized, and the reproducibility of the drive waveform can beimproved.

In the first embodiment, the voltage waveform applied to the actuator 8is filtered and then is applied to the digital signal processing unit120, and the above-described operation is performed by digitalprocessing to control the output switch. Examples of the digital signalprocessing include a method of using a random logic such as a FPGA(field-programmable gate array) and a method of performing processingusing a DSP (digital signal processor) or a CPU (central processingunit) and a program. The signal processing using a program has a highdegree of freedom for control but has a disadvantage in that theprocessing speed is slow. When a random logic is used, signal processingcan be performed at a high speed, and there is an advantage in that theswitching frequency is high.

FIGS. 16A to 16C are graphs illustrating the results of a simulationperformed by providing a dead band where both the high side switch SW1and the low side switch SW2 are switched off. The target drive waveformWCOM has a trapezoidal shape including a slope where a voltage isincreased or decreased, in which a maximum amplitude is 18 V and aninclination of the slope is 3.2 V/μs. A range where A≈B as the dead bandis ±50 mV. FIG. 16A illustrates the triangular wave Tri and the errordWCOM, FIG. 16B illustrates the output ACOM from the switching circuit110 and a current of the inductor L, and FIG. 16C illustrates the targetdrive waveform WCOM and the drive waveform COM. In addition, for acomparison, FIGS. 17A and 17B illustrate the result of a simulation whena dead band is not provided. As can be seen from FIGS. 16A to 17B,unnecessary switching can be suppressed by providing the dead band.Further, feedback is stabilized, and the reproducibility of the drivewaveform COM is high.

According to the first embodiment, during the period when the absolutevalue of the error dWCOM between the target drive waveform WCOM and thecomparative drive waveform dCOM is in a predetermined range, the deadband where both the high side switch SW1 and the low side switch SW2 areswitched off is provided. As a result, unnecessary switching of theoutput switch that may be performed when the drive waveform COM is inthe vicinity of the target drive waveform WCOM can be suppressed, andpower consumption can be reduced. In particular, not only when thevoltage of the target drive waveform WCOM is at a flat portion but alsowhen the voltage of the target drive waveform WCOM is at an inclined(dV/dt) slope where the voltage is increased or decreased, unnecessaryswitching can be suppressed.

Second Embodiment

Next, the liquid ejecting device 1 according to a second embodiment willbe described by using the ink jet head 1A as an example. FIG. 18 is anoverall circuit diagram illustrating an ink jet head drive circuit 200.That is, the ink jet head 1A according to the second embodiment is thesame as the ink jet head 1A according to the first embodiment, exceptthat a circuit configuration of the ink jet head drive circuit 200 isdifferent from that of the first embodiment. As illustrated in FIG. 18,the ink jet head drive circuit 200 includes the head drive circuit 7, aswitching type common drive waveform generation circuit 201, and theload counting circuit 102. The head drive circuit 7 and the loadcounting circuit 102 are the same as those of the first embodiment. Inaddition, for the common drive waveform generation circuit 201, the samecomponents as those in the first embodiment will be represented by thesame reference numerals, and the detailed description will not berepeated.

The common drive waveform generation circuit 201 that generates thedrive waveform COM as the common drive waveform includes: a firstswitching circuit 107A and a second switching circuit 107B as outputswitches; a first inductor L1 and a second inductor L2; the feedbackline and the filter 108 as an example of the voltage waveform detectionunit that detects the voltage waveform COM to be applied to the actuator8; and a digital signal processing unit 220. The filter 108 filters thedetected voltage waveform. The capacitor Cc is a stabilizing capacitorfor stabilizing the feedback control.

The digital signal processing unit 220 further includes the waveformmemory 103 as a storage unit of the target drive waveform WCOM, thesubtraction/comparison unit 104 as an arithmetic circuit, a firstcomparator 105A, a second comparator 105B, the A/D converter 109, and adetermination circuit 111. That is, the common drive waveform generationcircuit 201 according to the second embodiment includes two sets ofcircuits including the comparator 105, the switching circuit 107, andthe inductor L (A or B is added to the end of each of the referencenumerals). The first comparator 105A functions as a first pulse widthmodulation circuit, and the second comparator 105B functions as a secondpulse width modulation circuit. Further, the first switching circuit107A includes a first gate driver circuit 110A, a first high side switchSW1A connected to the power supply Vdd, and a first low side switch SW2Aconnected to the ground. The second switching circuit 107B includes asecond gate driver circuit 110B, a second high side switch SW1Bconnected to the power supply Vdd, and a second low side switch SW2Bconnected to the ground.

The circuit including the first comparator 105A, the first switchingcircuit 107A, and the first inductor L1 is used when the load is low.The circuit including the second comparator 105B, the second switchingcircuit 107B, and the second inductor L2 is used when the load is high.Therefore, the inductance of the second inductor L2 is lower than theinductance of the first inductor L1 (L2<L1). Further, it is preferablethat the capacitance of a transistor used for the second high sideswitch SW1B and the second low side switch SW2B (of the second switchingcircuit 107B) is higher than that of a transistor used for the firsthigh side switch SW1A and the first low side switch SW2A (of the firstswitching circuit 107A). In addition, the amplitudes of a triangularwave Tri to be applied to the first comparator 105A and a triangularwave Tri to be applied to the second comparator 105B may be the same aseach other but are preferably set to values such that an appropriatesensitivity can be obtained. In this embodiment, the inductors areswitched depending on the number of loads. A time required to charge anddischarge the load depends on both the size of the load and theinductance of the inductor. Therefore, unlike the first embodiment, whenthe load is high, the amplitude of the triangular wave Tri is notnecessarily reduced to increase the sensitivity of PWM. For example, theamplitude of the triangular wave Tri to be applied to the firstcomparator 105A is set to be lower than that of the triangular wave Trito be applied to the second comparator 105B. That is, contrary to thefirst embodiment, the amplitude of the triangular wave Tri on the secondinductor L2 side used when the load is high is lower than the amplitudeof the triangular wave Tri on the first inductor L1 side used when theload is low.

The determination circuit 111 determines whether to drive the circuit onthe first inductor L1 side or the circuit on the second inductor L2 sidedepending on the number of loads. For example, a threshold (for example,when the total number of nozzles 51 is 1200, the threshold is 600 orhalf of the total number of nozzles) of the number of loads is provided.When the number of actuators 8 driven during the same period is lessthan or equal to the threshold, the circuit on the first inductor L1side is selected. When the number of actuators 8 driven during the sameperiod is more than the threshold, the circuit on the second inductor L2side is selected. The determination circuit 111 outputs a control signalHPsel for setting the circuit on the inductor side to be used to beactive based on the determination result and applies the control signalHPsel to the first or second gate driver circuit 110A or 110B.

When the load is low, the circuit on the first inductor L1 side isselected, and charge is supplied to the actuator 8. Conversely, when theload is high, the circuit on the second inductor L2 side having a lowerinductance than the first inductor L1 is selected, and charge issupplied to the actuator 8. That is, when the load is high, there may bea case where the first inductor L1 cannot supply the required amount ofcharge during the required period as compared to the second inductor L2.However, the second inductor L2 supplies a larger amount of charge thanthe first inductor L1 during a predetermined period. Therefore, a highercurrent (ICOM2>ICOM1) than that of the first inductor L1 flows such thatcharge can be supplied to the actuator 8.

On the other hand, in the second inductor L2, the current rises moresteeply than the first inductor L1. Therefore, in a case where the loadis low, when the circuit on the second inductor L2 side is selected, theripple of the output may increase. In addition, there is a limit on theminimum ON time of the transistor used as the high side switches SW1Aand SW1B and the low side switches SW2A and SW2B. The limit value of theminimum ON time increases as the capacitance of the transistorincreases. Therefore, when the load is low, there may be a case wherestable driving cannot be performed in the circuit on the second inductorL2 side. By reducing the frequency of PWM, the ON duty can be reducedeven when the minimum ON time of the transistor is long. However, whenthe frequency of PWM is reduced, the reproducibility of the drivewaveform COM deteriorates, which may affect ink ejectioncharacteristics. Accordingly, according to the second embodiment, theseproblems are solved by selectively using the two inductors L1 and L2depending on the number of loads. That is, the actuators 8 as capacitiveloads can be stably driven irrespective of whether the number ofactuators 8 driven during the same period is small or large. As aresult, the reproducibility of the drive waveform COM capable of PWMdriving at a higher frequency can be improved, and ejectioncharacteristics can be improved.

Further, by using the two inductors L (L1, L2), the capacitance value ofthe stabilizing capacitor Cc can be made to be low, and thus powerconsumption can be reduced. By increasing the number of the inductors Lhaving different inductances and the number of drive circuits thereof tothree or four, the capacitance value of the stabilizing capacitor Cc canbe made to be lower. Therefore, power consumption can be furtherreduced, and the drive waveform COM can be accurately controlled. Inaddition, heat generation and a temperature increase can be suppressed.

Third Embodiment

Next, the liquid ejecting device 1 according to a third embodiment willbe described by using the ink jet head 1A as an example. FIG. is anoverall circuit diagram illustrating an ink jet head drive circuit 300according to a third embodiment. That is, the ink jet head 1A accordingto the third embodiment is the same as the ink jet head 1A according tothe first embodiment or the second embodiment, except that a circuitconfiguration of the ink jet head drive circuit 300 is different fromthat of the first embodiment or the second embodiment. As illustrated inFIG. 19, the ink jet head drive circuit 300 includes the head drivecircuit 7, a switching type common drive waveform generation circuit301, and the load counting circuit 102. The head drive circuit 7 and theload counting circuit 102 are the same as those of the first embodimentor the second embodiment. In addition, for the common drive waveformgeneration circuit 301, the same components as those in the firstembodiment will be represented by the same reference numerals, and thedetailed description will not be repeated.

The common drive waveform generation circuit 301 that generates thedrive waveform COM as the common drive waveform is configured bycombining the functions of the common drive waveform generation circuit101 according to the first embodiment and the common drive waveformgeneration circuit 201 according to the second embodiment. That is, thecommon drive waveform generation circuit 301 includes: the firstswitching circuit 107A and the second switching circuit 107B as outputswitches; the first inductor L1 and the second inductor L2; the feedbackline 113 and the filter 108 as an example of the voltage waveformdetection unit that detects the voltage waveform COM to be applied tothe actuator 8; and a digital signal processing unit 320. The filter 108filters the detected voltage waveform. The capacitor Cc is a stabilizingcapacitor for stabilizing the feedback control.

The digital signal processing unit 320 further includes the waveformmemory 103 as a storage unit of the target drive waveform WCOM, thesubtraction/comparison unit 104 as an arithmetic circuit, the firstcomparator 105A, the second comparator 105B, the triangular wavegeneration circuit 106, the A/D converter 109, and the determinationcircuit 111. Further, the first switching circuit 107A includes thefirst gate driver circuit, the first high side switch SW1A connected tothe power supply Vdd, and the first low side switch SW2A connected tothe ground. The second switching circuit 107B includes the second gatedriver circuit, the second high side switch SW1B connected to the powersupply Vdd, and the second low side switch SW2B connected to the ground.

In the above-described circuit, the load counting circuit 102 counts thenumber of actuators 8 being driven during the same period. This countednumber of actuators 8 is used as the number of loads. The load countingcircuit 102 supplies the counted number of actuators 8 to thedetermination circuit 111 as the load number information. Thedetermination circuit 111 determines whether to drive the circuit on thefirst inductor L1 side or the circuit on the second inductor L2 sidedepending on the number of loads, outputs the control signal HPsel forsetting the circuit on the inductor side to be driven to be active, andapplies the control signal HPsel to the first or second gate drivercircuit 110A or 110B through a gate circuit 112A or 112B. The controlsignal HPsel is input to the gate circuit 112A by a negative logic andis input to the gate circuit 112B by a positive logic. Therefore, whilethe control signal HPsel is at an L level, the first gate driver circuitis active, and while the control signal HPsel is at an H level, thesecond gate driver circuit is active. Further, the load numberinformation is applied to the triangular wave generation circuit 106.The triangular wave generation circuit 106 generates the triangular waveTri having an amplitude adjusted according to the number of loads andapplies the triangular wave Tri to the first or second comparator 105Aor 105B on the side to be driven. For example, the determination circuitroughly classifies the number of loads and determines whether to drivethe circuit on the first inductor L1 side or the circuit on the secondinductor L2 side depending on the number of loads as in the secondembodiment. In either case, depending on the number of loads, as in thefirst embodiment, when the number of loads is large (that is, when thetotal load is high), the amplitude of the triangular wave Tri isdecreased; and when the number of loads is small (hat is, when the totalload is low), the amplitude of the triangular wave Tri is increased.

In addition, when the absolute value of the error dWCOM between thetarget drive waveform WCOM and the comparative drive waveform dCOM is ina predetermined range (including when no error is present), thesubtraction/comparison unit 104 outputs an H level as a stop signal froman output terminal (A≈B).

The stop signal is input to one input terminal of the gate circuit 112A.The control signal HPsel is applied to the other input terminal of thegate circuit 112A. When one input is at an H level or the other input isat an H level, the gate circuit 112A sets an output disable 1 signal asthe H level. While at least the H level as the stop signal is outputfrom the output terminal (A≈B), the disable 1 signal is at the H level.While the disable signal is at the H level, the first gate drivercircuit 110A turns off the first high side switch SW1A and the first lowside switch SW2A.

The stop signal is input to one input terminal of the gate circuit 112B.The control signal HPsel is applied to the other input terminal of thegate circuit 112B. When one input is at an H level or the other input isat an H level, the gate circuit 112B sets an output disable 2 signal asthe H level. While at least the H level as the stop signal is outputfrom the output terminal (A≈B), the disable 2 signal is at the H level.While the disable signal is at the H level, the first gate drivercircuit 110B turns off the first high side switch SW1B and the first lowside switch SW2B.

According to the third embodiment, the functions of the common drivewaveform generation circuit 101 according to the first embodiment andthe common drive waveform generation circuit 201 according to the secondembodiment are combined. As a result, the two inductors L1 and L2 can beselectively used depending on the number of loads, the sensitivity ofPWM can be finely adjusted depending on the number of loads, and thusfeedback is stable in a wider range. Further, by providing a dead bandwhere switching is stopped, unnecessary switching can be reduced, andpower consumption can be reduced.

Fourth Embodiment

FIG. 20 illustrates an ink jet head drive circuit 400 according to afourth embodiment. The ink jet head drive circuit 400 according to thefourth embodiment is a modification example in which a dead band inwhich the switching of the output switch is stopped is added to the inkjet head drive circuit 200 of the second embodiment. That is, when theabsolute value of the error dWCOM is in a predetermined range as aresult of the subtraction comparison (including when no error ispresent), the subtraction/comparison unit 104 according to themodification example outputs a disable signal as a stop signal from anoutput terminal (A≈B). The disable signal is applied to the first orsecond gate driver circuit 110A or 110B on whichever side is currentlybeing used through the gate circuit 112A or 112B. The first or secondgate driver circuit 110A or 110B to which the disable signal is appliedturns off the first or second high side switch SW1A or SW1B and thefirst or second low side switch SW2A or SW2B. That is, the switching ofthe output switch is stopped. This way, by providing a dead band inwhich switching of the output switch is stopped, unnecessary switchingthat might otherwise be performed when the drive waveform COM is nearthe target drive waveform WCOM can be suppressed, and power consumptioncan be reduced.

In a modification example of ink jet head 1A, as illustrated in FIG. 21,the nozzle plate 5 may directly communicate with the common ink chamber42 without providing an individual pressure chamber 41.

In the above-described embodiments, the ink jet heads 1A and 101A of anink jet printer 1 were described as an example of a liquid ejectingdevice. However, the liquid ejecting device may be a material ejectionhead of a 3D printer or a sample ejection head of a liquid dispensingdevice. In such cases, references to “image data” can be consideredequivalent to “pattern data” in the context of a 3D printer or moregenerally “intended output data” in the context of a liquid ejectiondevice. In general, particular configuration and arrangement of aspectsand components for the above-described embodiments are not particularlylimited as long as the actuator 8 is a capacitive load. Furthermore, insome examples, pulse-density modulation (PDM) may be adopted instead ofpulse width modulation (PWM).

In addition, the numbers of the nozzles 51 and the actuators 8constituting the channel are not necessarily plural. That is, the commondrive waveform generation circuit 101, 201, or 301 functions as thedrive waveform generation circuit that applies the drive waveform to theactuator 8.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A drive circuit for a liquid ejecting device,comprising: a first switch connected between a first potential and anoutput terminal, the output terminal connected to an actuator of aliquid ejecting device and outputting a drive signal waveform to theactuator; a second switch connected between the output terminal and asecond potential lower than the first potential; and a signal processingcircuit configured to control the first switch and the second switchaccording to an absolute value of a difference between a target drivewaveform and a detected voltage waveform of the drive signal waveform atthe output terminal, the first and second switch being off when theabsolute value of the difference is less than a threshold value.
 2. Thedrive circuit according to claim 1, wherein the signal processingcircuit is configured to: cause the first switch to be turned on and offduring charging of the actuator when the absolute value of thedifference is greater than the threshold value; and cause the secondswitch to be turned on and off during discharging of the actuator whenthe absolute value of the difference is greater than the thresholdvalue.
 3. The drive circuit according to claim 1, wherein the signalprocessing circuit is configured to: cause the first switch to be turnedon and off during charging of the actuator such that the absolute valueof the difference is reduced; and cause the second switch to be turnedon and off during discharging of the actuator such that the absolutevalue of the difference is reduced.
 4. The drive circuit according toclaim 3, wherein when the absolute value of the difference is less thanthe threshold value, the drive signal waveform is output through theoutput terminal without the first or second switches being turned on. 5.The drive circuit according to claim 1, further comprising: a switchingcircuit configured to select a portion of a waveform of the drive signalwaveform to be applied to different actuators for liquid ejection. 6.The drive circuit according to claim 1, further comprises: a gate drivercircuit configured to control switching of the first and secondswitches, wherein the signal processing circuit is configured to disablethe gate driver circuit when the absolute value of the difference isless than the threshold value.
 7. The drive circuit according to claim1, further comprising: a third switch connected between a thirdpotential and the output terminal; and a fourth switch connected betweenthe output terminal and a fourth potential lower than the thirdpotential, wherein the signal processing circuit is further configuredto control the third switch and the fourth switch to be off when theabsolute value of the difference is less than the threshold value. 8.The drive circuit according to claim 7, wherein the signal processingcircuit is further configured to: cause the first switch to be turned onand off and the third switch to be off during charging of actuators in afirst mode when the absolute value of the difference is greater than thethreshold value; cause the second switch to be turned on and off and thefourth switch to be off during discharging of the actuators in the firstmode, when the absolute value of the difference is greater than thethreshold value; cause the third switch to be turned on and off and thefirst switch to be off during charging of the actuators in a second modewhen the absolute value of the difference is greater than the thresholdvalue; and cause the fourth switch to be turned on and off and thesecond switch to be off during discharging of the actuators in thesecond mode when the absolute value of the difference is greater thanthe threshold value.
 9. The drive circuit according to claim 8, whereina first drive signal based on a triangle wave of a first amplitude isoutput at the output terminal in the first mode, and a second drivesignal based on a triangle wave of a second amplitude greater than thefirst amplitude is output at the output terminal in the second mode. 10.The drive circuit according to claim 7, wherein the first and secondswitches are connected to the output terminal through a first inductor,and the third and fourth switches are connected to the output terminalthrough a second inductor having an inductance less than the firstinductor.
 11. A liquid ejection device, comprising: a nozzle plateincluding a plurality of ejection nozzles; a plurality of actuatorscorresponding to the plurality of ejection nozzles; and a drive circuitconfigured to drive the plurality of actuators, the drive circuitcomprising: a first switch connected between a first potential and anoutput terminal, the output terminal connected to an actuator andoutputting a drive signal waveform to the actuator; a second switchconnected between the output terminal and a second potential lower thanthe first potential; and a signal processing circuit configured tocontrol the first switch and the second switch according to an absolutevalue of a difference between a target drive waveform and a detectedvoltage waveform of the drive signal waveform at the output terminal,the first and second switch being off when the absolute value of thedifference is less than a threshold value.
 12. The liquid ejectiondevice according to claim 11, wherein the signal processing circuit isconfigured to: cause the first switch to be turned on and off duringcharging of the actuator when the absolute value of the difference isgreater than the threshold value; and cause the second switch to beturned on and off during discharging of the actuator when the absolutevalue of the difference is greater than the threshold value.
 13. Theliquid ejection device according to claim 11, wherein the signalprocessing circuit is configured to: cause the first switch to be turnedon and off during charging of the actuator such that the absolute valueof the difference is reduced; and cause the second switch to be turnedon and off during discharging of the actuator such that the absolutevalue of the difference is reduced.
 14. The liquid ejection deviceaccording to claim 13, wherein when the absolute value of the differenceis less than the threshold value, the drive signal waveform is outputthrough the output terminal without the first or second switches beingturned on.
 15. The liquid ejection device according to claim 11, whereinthe drive circuit further comprises: a switching circuit configured toselect a portion of a waveform of the drive signal waveform to beapplied to different actuators for liquid ejection.
 16. The liquidejection device according to claim 11, further comprising: a gate drivercircuit configured to control switching of the first and secondswitches, wherein the signal processing circuit is configured to disablethe gate driver circuit when the absolute value of the difference isless than the threshold value.
 17. The liquid ejection device accordingto claim 11, further comprising: a third switch connected between athird potential and the output terminal; and a fourth switch connectedbetween the output terminal and a fourth potential lower than the thirdpotential, wherein the signal processing circuit is further configuredto control the third switch and the fourth switch to be off when theabsolute value of the difference is less than the threshold value. 18.The liquid ejection device according to claim 17, wherein the signalprocessing circuit is further configured to: cause the first switch tobe turned on and off and the third switch to be off during charging ofactuators in a first mode when the absolute value of the difference isgreater than the threshold value; cause the second switch to be turnedon and off and the fourth switch to be off during discharging of theactuators in the first mode, when the absolute value of the differenceis greater than the threshold value; cause the third switch to be turnedon and off and the first switch to be off during charging of theactuators in a second mode when the absolute value of the difference isgreater than the threshold value; and cause the fourth switch to beturned on and off and the second switch to be off during discharging ofthe actuators in the second mode when the absolute value of thedifference is greater than the threshold value.
 19. The liquid ejectiondevice according to claim 18, wherein a first drive signal based on atriangle wave of a first amplitude is output at the output terminal inthe first mode, and a second drive signal based on a triangle wave of asecond amplitude greater than the first amplitude is output at theoutput terminal in the second mode.
 20. The liquid ejection deviceaccording to claim 17, wherein the first and second switches areconnected to the output terminal through a first inductor, and the thirdand fourth switches are connected to the output terminal through asecond inductor having an inductance less than the first inductor.